Apparatus for reducing smoke emission from elevated flare stacks



Dec. 22, 1964 Filed May 29, 1961 ELEVATED FLARE STACKS 3 Sheets-Sheet l 2 LL l3 7 INVENTOR- CHARLES AVALON'H/NVEST WILLIAMS ATTORNEYS 1964 c. A. H. WILLIAMS APPARATUS FOR REDUCING SMOKE EMISSION FROM ELEVATED FLARE STACKS Filed May 29, 1961 3 Sheets-Sheet 2 INVENTOR CHARLES AVALON HINVEST WILLIAMS By Wary) FWM FMAMI: ,5

ATTOR NE Y5 1964 c. A. H. WILLIAMS 3, 62,

APPARATUS FOR REDUCING SMOKE EMISSION FROM ELEVATED FLAREESTACKS Filed-May 29, 1961 3 Sheets-Sheet 3 INVENTOR CHARLES AVALON HINVEST WILLIAMS ATTORNEYS United States Patent 3,162,236 APPARATUS FGR MDUfilNG SMGKE EMISSHGN FRUM ELEVATED FLARE STACKS Charles Avalon i'linvest Williams, London, England, as-

signor to The British Petroleum Company Limited, London, England, a British joint-stock corporation Filed May 29, 1961, Ser. No. 113,519 Claims priority, application Great Britain June 3, 1960 3 Claims. ((35. 158-99) This invention relates to water injection equipment, suitable for use on elevated flare stacks. By elevated flare stacks we mean flare stacks of suflicient height to render the position of the combustion zone thereof sensitive to wind effects. Such stacks are usually greater than 30 feet in height.

In the refining of mineral oils, particularly petroleum oils, there are usually produced and/or separated from the oils, gases comprising hydrocarbons having from one to three carbon atoms per molecule. While it is possible to utilise these gases, or components of these gases, either in hydrocarbon conversion reactions, for example polymerisation, or as a works fuel, there will usually be a fluctuating surplus make which cannot be absorbed in this manner and it is customary to burn off this surplus gas at the head of a flare stack, which may be an elevated flare stack. The rate of flaring of such gases will nor mally be low.

The same flare stack is usually employed for the combustion of gases which may be released suddenly 'as a result of an emergency, for example the failure of a refinery processing unit, and which must be disposed of speedily and safely. Such gases will generally contain large proportions of hydrocarbons having from three to five carbon atoms per molecule and/or large proportions of unsaturated hydrocarbons. The rate of flaring of such gases may, on occasion, he very high.

Flare stacks, if unmodified, in normal operation generally produce quantities of black smoke and of oxygenated hydrocarbon irritants. The conditions which give rise to these unpleasant effects, including an inadequate supply of combustion air, the presence of hydrocarbon gases of high molecular weight and/or in the presence of olefinic and/ or acetylenic hydrocarbon gases, are greatly aggravated during emergency flaring.

It is always desirable and frequently essential, because of legislation, to minimise and, if possible, to eliminate the amount of smoke emitted by a flare. Smoke formation may be reduced by improving the degree of combustion of stack gases by increasing the quantity of air in admixture with the stack gases before and during combustion. Complete combustion will ensure complete elimination of smoke.

Various modification to flare stacks, designed to achieve more complete combustion of stack gases have been described in the prior art. it is known, for example, that the injection of requisite quantities of air into the stack by means of a mechanical blower results in the production of a combustion mixture having suflicient oxygen available for complete combustion of stack gases under normal circumstances. Blowers are costly, however, and it is not economically possible to provide that extra blower capacity which would be required in a major emergency. It is also known to induct combustion air into the stack by means of the venturi principle, but this method involves operating the stack under relatively high pressures, from l3 p.s.i.g., and increases the danger of a flash-back occurring within the stack. It is also known to inject steam into the stack but this method suffers from the disadvantage that large quantities of a valuable product are lost. It has been estimated that a flaring rate of 12.2 million cubic feet per day of stack gases grass Patented Dec. 22, 1964 would require the provision of 50,000 pounds per hour of steam.

Ground flares have been described in which the mixing of stack gases and combustion air has been satisfactorily achieved by the use of Water injection apparatus which directs a spray of water into the combustion zone of the stack. Such a method of mixing is eflicient, simple and cheap, there being no expensive equipment involved. Because of fire hazards, ground flares cannot be sited as close to plant units as can elevated flares. Ground flares therefore require surrounding safety zones to be of large extent and prevent the more economic exploitation of such areas.

Previous attempts to apply water injection to elevated flare stacks have been made but failed because of the difliculty of maintaining the water spray in the combustion zone at the top of a Wind exposed stack, the zone tending to strike down the leeward side of the stack and away from the spray.

We have now discovered equipment for applying Water injection successfully to elevated flare stacks.

The economic advantages of this discovery will be obvious.

It is an object of this invention to provide an elevated flare stack which will burn stack gases with a smoke reduced flame.

t is a further object to provide a water cooled flare stack burner head unit.

Thus according to one aspect of this invention there is provided apparatus, for use on elevated flare stacks, comprising, in combination, a burner head unit fitted with a nozzle, adapted to direct an atomised spray of water into the combustion zone of the burner head unit, and a wind deflector, adapted to be set about the burner head unit in such manner that air is deflected to the leeward side of the stack under Windy conditions.

\ of Water into the combustion zone of the burner head unit, the nozzle being fitted with a cowl and a drainage tray, thecowl being adapted to return water to the drainage tray, (1)) a storage tank adapted to receive water from the drainage tray, (c) a pump adapted to take suction from the storage tank and to deliver at the nozzle, and (d) a wind deflector adapted to be set about the burner head unit in such manner that air is deflected to the leeward side of the stack under windy conditions.

Preferably the nozzle is a centrifugal spray type nozzle.

Preferably the nozzle is adapted to direct the spray in an upward direction.

It has been found that water effectively cools the burner head unit, thus obviating the need to use high tempera ture resistant alloys in the construction of the burner head unit.

The burner head unit, nozzle and Wind deflectors are preferably made of steel, mild steel being quite suitable. Most preferably the burner head unit is tipped with stainless steel. A protective internal lining of a refractory material reinforced by metal may be fitted within the burner head unit.

Preferably means are provided whereby the flow of water to the nozzle may be correlated with the flow of gases to the stack.

Preferably the wind deflector is as described in British patent specification 795,664 and comprises a plurality of vertical slats adapted to be set about the burner head in such manner that each slat is spaced from adjacent slats and from the burner head, whereby air is deflected to the leeward side of the stack under differing wind directions, each of the slats having its broad faces tapered at the formation and results in the emission of smoke.

a closed system it is convenient to use a small pump of low capacity and high head to prime the system and make up losses and to use a large pump of high capacity and low head to provide the flow of water to the spray nozzle.

Nozzles suitable for supplying water in the varying quantities required for use in conjunction with a given range of gas flaring rates may be designed and constructed by standard engineering techniques.

The quantity of water required will vary both with the quantity and the quality of the gas to be flared. An increase in the rate of flaring of gases will demand an increase in the rate of supply of water. An increase in the proportion of unsaturated molecules present in the gases will also demand an increase in the rate of supply of water.

Water supplied in excess of the quantity required to give a smokeless flame will reduce the luminosity of the flame and may give rise to the formation of evil smelling .aldehydes. V v

There follows a-discussion of the theoreticalprinciples involved.

Stack gases discharged from an unmodified flare stack have not been pre-mixed with air and combustion of the gases occurs in air and not in a combustible mixture of gas and air. This means that insuflicient air is available for complete combustion and the resulting deficiency promotes carbon formation. In addition, the heat gen- FIG. 2 is a schematic plan view, mostly in section, along the line 22 of FIG. 1.

FIG. 3 is a schematic view which shows the structure of FIGURES 1 and 2 attached/co a flare stack body 15, a storage 16 and apump 17.

With reference to FIGURES 1 and 2:

The burner head unit consists of two cylindrical coaxial pipes land 2, the diameter of 2 being less than that of 1. The lower end of 1 is co-planar with the upper end of 2. An annular space 3 is thereby formed. The

pipes 1 and 2 are supported by struts 4. To the lower end of the pipel is bolted 'a tray 5 having an annular depression 6 drained by a line 7.

erated by incomplete combustion of the gases tends to cause cracking and polymerisation of unburned gases with the subsequent formation of 'olefins and possibly hydrocarbons of high molecular weight. The partial combustion of such compounds further increases carbon combustion of stack gases may also form hydrogen and/ or a reducing atmosphere, both of which favour the formation of carbon particles and smoke when the ply of combustion air is insuflicient.

Partial SU P- Avoidance of smoke emission can only be obtained by complete combustion of the stack gases. Thisrequires a high air to gas ratio which is best achieved by turbulent adrmxture of air and gases.

A spray nozzle appropriately situated in the burner head of a flare'stack and discharging aco-nical spray of a-tomised water into stack gases in the burner head will produce turbulence in the gas stream issuing from the stack. 'Consequently, surrounding air will rapidly diffuse into the turbulent gases. Turbulence isfurther intion with the resulting formation of carbon monoxidean'dr hydrogen, both of which burn with a smokeless flame,

when the supply of combustion air is sufficient.

The invention .is illustrated by but not limited with reference to the figures of the accompanying drawings 'FIG. 1 is a schematic elevation, mostly in section,

along the line 1--1--of FIG; 2.; It differs from a true sectional elevation in thatthe nozzle 12 and its supply line 13 are not shown in section, 1

Clamp rings 8,9 and 10 are welded to the pipe 1., A plurality of metal slats 11 are spaced uniformly about the burner head and are secured to the clamp rings 8, 9 and 10 and to the tray 5. Theupper extremity of each of the slats 11 is tapered and the tapered sections are curved towards the pipe 1.

A centrifugal spray nozzle 12, supplied with water by a line 13, is inserted into the pipe 2. The nozzle 12 is surrounded by a co'wl 14 comprising an upper cylindrical section and, below the nozzle, a lower frusto-conical section contiguous with the outer wall of the depression 6. The line 13 is supplied with water from tank 16 by means of the pump 17. The line 7 returns water to the tank 16.

A gas pilot line 18 and a flame propagation tube 19 project into the pipe 1.-

In use, stack gases pass up through the center opening in. tray 5 and then through the pipes 2 and 1. An amount of combustion air is induced into the pipe 1 through the annulus 3 and is thoroughly admixed with stack gases by means of the turbulence produced by a spray ofatomised water generated by the nozzle 12. The mixing effect of this turbulence within the pipe 2 is felt outside the pipe and more combustion air thereby diffuses into the combustion zone of the burner head unit. Combustion is initiated by the propagation tube 16 and the continuance of combustion is ensured by an auxiliary supply of combustible gas through the line 15. Unatomised water'impinges on the wall of the co wl 14 and is collected in the depression 6 from which it is removed by the line 7 to be recycled;

I claim:

1. In an elevated flare stack arrangement having water injection apparatus positioned-at the top of said flare stack, said water injection'apparatus comprising in combination, (a) a burnerhead unit comprising: pipe means adapted to receive discharged gases from a flare stack, said pipe means providing a combustion zone for said gases, a nozzle located in the pipe means below'the combustion zone and adapted to direct an atomized spray of water in an upward direction into the combustion zone, and means adapted for'the admission of air into the combustion zone and .(b) a wind deflector adapted to set about the burner head unit in such manner that air is deflected to the leeward side of the stack under windy' conditions.

. 2. In an elevated flare stack arrangement according to claim .1 wherein the nozzle is a'centrifugalspray type nozzle.

3. In an elevated flare-stack arrangement havingwater injection apparatus positioned at the'top of said flare stack, said waterinjeotionapparatus comprising incom-v bination, (a) a burner head unit comprising: pipe means water inan upward direction into the'combustion zone,

the nozzle being fitted ;with acowl and drainage tray,

the cowl being adapted to return waterto the drainage tray, and means adapted for admission of air into the combustion zone, (b) a storagetank adapted to receive water from the drainage tray, (c) a' pump adapted to take suction from the storage tankiandto deliver at the nozzle.

5 and (d) a wind deflector adapted to be set about the burner head unit in suchv manner that air is deflected to the leeward side of the stack under windy conditions.

References Cited in the file of this patent 5 UNITED STATES PATENTS 545,023 Lord Aug. 20, 1895 6 Breitwieser Aug. 19, 1930 Zink et a1. Jan. 29, 1957 Smith Apr. 15, 1958 Kocee June 2, 1959 Winkler Oct, 27, 1959 FOREIGN PATENTS Great Britain May 28, 1958 

1. IN AN ELEVATED FLARE STACK ARRANGEMENT HAVING WATER INJECTION APPARATUS POSITIONED AT THE TOP OF SAID FLARE STACK, SAID WATER INJECTION APPARATUS COMPRISING IN COMBINATION, (A) A BURNER HEAD UNIT COMPRISING: A PIPE MEANS ADAPTED TO RECEIVE DISCHARGED GASES FROM A FLARE STACK, SAID PIPE MEANS PROVIDING A COMBUSTION ZONE FOR SAID GASES, A NOZZLE LOCATED IN THE PIPE MEANS BELOW THE COMBUSTION ZONE AND ADAPTED TO DIRECT AN ATOMIZED SPRAY OF WATER IN AN UPWARD DIRECTION INTO THE COMBUSTION ZONE AND MEANS ADAPTED FOR THE ADMISSION OF AIR INTO THE COM- 